This invention relates generally to improvements in video recorder-playback machines, and more specifically to an improved arrangement of optical components in a video recorder-playback machine of the type including optical laser beams for recording and playback of video information from a video information disc.
Video recorder-playback machines in general are known in the art and include appropriate means for recording and/or playing back a video information signal utilizing a selected medium for storage of the signal. For example, in one type of machine, the video signal is recorded magnetically for storage and/or retrieval upon a length of so-called video tape. In another type of system, the video signal is recorded upon an information disc for retrieval by means of a stylus, in a manner analogous to that of sound reproduction from phonographic records. In still another type of system, the video signal is used to frequency modulate a beam of amplified light, such as a laser beam, with sufficient power for physically altering the surface characteristics of a light sensitive coating on a video information disc and thereby record the signal upon the disc. During playback, a lower power light beam is reflected from the disc and the resulting signal is demodulated to reproduce the recorded signal. In all of these types of systems, the video information signal can be combined with an appropriate audio signal either for recording or playback purposes to yield a composite audio-video signal of the type commonly used for television transmissions and the like. For convenience, however, the signal will be referred to herein as a video information signal.
Video recorder-playback machines utilizing amplified light beams for recording and playback purposes offer significant advantages in that all physical contact of the recording and playback elements with the storage medium, namely, the information disc, is avoided. This prevents wear and deterioration of the machine elements and the disc, resulting in a high quality stored video signal which can be played back repeatably over a long period of time with unimpaired video resolution.
In video recorder-playback machines using amplified light beams for signal recording and playback, separate laser generator units are provided for generating the high power record optical beam and the low power playback optical beam, respectively. These laser generator units thus comprise a "write" laser and a "read" laser and are mounted on the machine in optical alignment with an optical record-playback head including a focusing lens for focusing the beams upon the video information disc. Typically, the record-playback head is driven in a radial direction with respect to the disc simultaneously with rotation of the disc whereby the video information is recorded upon and played back from a spiral pattern of information tracks on the disc. Importantly, for maximum information storage together with maximum recording and playback time for each disc, it is desirable to form the information tracks to have a narrow width such as on the order of about 0.5 microns, and a narrow center-to-center radial spacing such as on the order of about 1.5 microns. Accordingly, a precise optical alignment between the laser generator units and the record-playback head is critical for proper focusing of the record and playback beams to a spot image within the information tracks in order to maximize signal resolution and minimize cross talk between tracks.
In the prior art, the "write" laser and the "read" laser are commonly mounted upon a fixed base of the recorder-playback machine. A plurality of redirecting mirrors and optical conditioning lenses are provided for aligning the generated record and playback optical beams with the movable record-playback head. See, for example, U.S. Pat. Nos. 3,908,076; 3,908,080; and 3,924,062 and copending U.S. application Ser. No. 094,108, filed Nov. 14, 1979. However, these systems require a relatively large number of mirrors, etc. which must be adjusted manually to the proper position for achieving the necessary precise alignment of the beams with the record-playback head. This results in a system which is relatively complex, bulky, expensive, and difficult to maintain in proper adjustment. Accordingly, such systems have not found commercial acceptance in production quantities.
A few prior art playback machines have been proposed wherein the relatively small "read" laser is mounted in fixed optical alignment with a playback head for movement together upon an optics carriage. See, for example, U.S. Pat. Nos. 3,829,622; 3,914,541; 3,944,727; and 3,947,888. While these types of arrangements advantageously simplify alignment of the playback optical beam with the head, such arrangements heretofore have been limited for use only in playback machines. Alternately stated, these arrangements have not been adapted for use in a recorder-playback machine wherein additional alignment of the record-playback head with a record beam generated by a "write" laser is also required.
The present invention comprises an improvement upon the prior art by providing a simplified and relatively compact mounting and alignment arrangement between the "write" and "read" lasers with an optical record-playback head in a video recorder-playback machine.